On Mar 16, 2013, at 7:01 PM, Andrew Werchowiecki 
<andrew.werchowie...@xpanse.com.au> wrote:

> It's a home set up, the performance penalty from splitting the cache devices 
> is non-existant, and that work around sounds like some pretty crazy amount of 
> overhead where I could instead just have a mirrored slog.
> I'm less concerned about wasted space, more concerned about amount of SAS 
> ports I have available.
> I understand that p0 refers to the whole disk... in the logs I pasted in I'm 
> not attempting to mount p0. I'm trying to work out why I'm getting an error 
> attempting to mount p2, after p1 has successfully mounted. Further, this has 
> been done before on other systems in the same hardware configuration in the 
> exact same fashion, and I've gone over the steps trying to make sure I 
> haven't missed something but can't see a fault. 

You can have only one Solaris partition at a time. Ian already shared the 
answer, "Create one 100% 
Solaris partition and then use format to create two slices."
 -- richard

> I'm not keen on using Solaris slices because I don't have an understanding of 
> what that does to the pool's OS interoperability. 
> ________________________________________
> From: Edward Ned Harvey (opensolarisisdeadlongliveopensolaris) 
> [opensolarisisdeadlongliveopensola...@nedharvey.com]
> Sent: Friday, 15 March 2013 8:44 PM
> To: Andrew Werchowiecki; zfs-discuss@opensolaris.org
> Subject: RE: partioned cache devices
>> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
>> boun...@opensolaris.org] On Behalf Of Andrew Werchowiecki
>> muslimwookie@Pyzee:~$ sudo zpool add aggr0 cache c25t10d1p2
>> Password:
>> cannot open '/dev/dsk/c25t10d1p2': I/O error
>> muslimwookie@Pyzee:~$
>> I have two SSDs in the system, I've created an 8gb partition on each drive 
>> for
>> use as a mirrored write cache. I also have the remainder of the drive
>> partitioned for use as the read only cache. However, when attempting to add
>> it I get the error above.
> Sounds like you're probably running into confusion about how to partition the 
> drive.  If you create fdisk partitions, they will be accessible as p0, p1, 
> p2, but I think p0 unconditionally refers to the whole drive, so the first 
> partition is p1, and the second is p2.
> If you create one big solaris fdisk parititon and then slice it via 
> "partition" where s2 is typically the encompassing slice, and people usually 
> use s1 and s2 and s6 for actual slices, then they will be accessible via s1, 
> s2, s6
> Generally speaking, it's unadvisable to split the slog/cache devices anyway.  
> Because:
> If you're splitting it, evidently you're focusing on the wasted space.  
> Buying an expensive 128G device where you couldn't possibly ever use more 
> than 4G or 8G in the slog.  But that's not what you should be focusing on.  
> You should be focusing on the speed (that's why you bought it in the first 
> place.)  The slog is write-only, and the cache is a mixture of read/write, 
> where it should be hopefully doing more reads than writes.  But regardless of 
> your actual success with the cache device, your cache device will be busy 
> most of the time, and competing against the slog.
> You have a mirror, you say.  You should probably drop both the cache & log.  
> Use one whole device for the cache, use one whole device for the log.  The 
> only risk you'll run is:
> Since a slog is write-only (except during mount, typically at boot) it's 
> possible to have a failure mode where you think you're writing to the log, 
> but the first time you go back and read, you discover an error, and discover 
> the device has gone bad.  In other words, without ever doing any reads, you 
> might not notice when/if the device goes bad.  Fortunately, there's an easy 
> workaround.  You could periodically (say, once a month) script the removal of 
> your log device, create a junk pool, write a bunch of data to it, scrub it 
> (thus verifying it was written correctly) and in the absence of any scrub 
> errors, destroy the junk pool and re-add the device as a slog to the main 
> pool.
> I've never heard of anyone actually being that paranoid, and I've never heard 
> of anyone actually experiencing the aforementioned possible undetected device 
> failure mode.  So this is all mostly theoretical.
> Mirroring the slog device really isn't necessary in the modern age.
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